Communication and/or Control Apparatus and Method for Detecting Locking States in Same

ABSTRACT

The invention concerns a method for detecting locking states in communication and/or control appliances (SG i ) dispersedly networked together by a data bus ( 2 ). Said method consists in comparing a message currently transmitted by a communication and/or control appliance (SG i ) to a previously transmitted message and determine the absence of a locking state of the communication and/or control appliance (SG i ) if the messages are different and in encoding a message counter with the transmitting communication and/or control appliance (SG i ) in the transmitted message if the messages are identical and decoding the message counter in a communication and/or control appliance (SG i ) receiving the message and determining the absence of locking state at the communication and/control appliance (SG i ) if the value of the message counter has changed relative to a previous value of the message counter of a previously transmitted message, and determining a locking state of the communication and/or control appliance (SG i ) if the message counter value has not changed after a specific waiting time (t w ).

BACKGROUND OF THE INVENTION

The invention relates to a method for detecting locking states incommunication and/or control apparatuses which are networked to oneanother in a distributed manner using a data bus.

The invention also relates to a communication and/or control apparatushaving an interface for connection to a data bus and networking tofurther communication and/or control apparatuses.

In complex technical systems in which communication and/or controlapparatuses are networked to one another via a data bus, the readinessto transmit and the functionality of the communication and/or controlapparatuses must be regularly monitored. This is indispensable, inparticular, for safety-critical applications in motor vehicles, forexample airbag control apparatuses etc.

To this end, it is first of all possible to evaluate whether messagesare regularly transmitted by the communication and/or controlapparatuses.

However, a problem arises when the communication and/or controlapparatuses are in a locking state and transmit messages even though thecommunication and/or control apparatus is blocked and can no longerperform its actual task. A locking state is a state in which twoprocesses which are respectively assigned an operating means are waitingfor the respective other process to enable the operating means, forexample, and both processes thus block one another. Although they arethus still able to regularly transmit messages, they are blocked fromcarrying out the actual process.

JP 11163905 A discloses a method for the multiplexed transmission ofdata via a data bus in a motor vehicle, in which changes in the data aredetected and are indicated using an update bit.

JP 11163903 A also discloses a method for the multiplexed transmissionof data via a data bus in a motor vehicle, in which the connection of acommunication unit of the calling subscriber to the data bus is detectedand the data are only then transmitted.

In the conventional methods, locking states are detected byconcomitantly transmitting, together with the message to be transmitted,a monitoring signal from the transmitter, for example a message counter.This additional information is not used to transmit function contents orfunction signals but merely for monitoring purposes in order to be ableto detect a possible locking state of the transmitting communicationand/or control apparatus in a communication and/or control apparatusthat receives the message. This additional information disadvantageouslyincreases the length of the message and disadvantageously increases thedata bus utilization level.

Therefore, it is an object of the invention to provide an improvedmethod for detecting locking states in communication and/or controlapparatuses which are networked to one another in a distributed mannerusing a data bus, the utilization level of the data bus being intendedto be reduced by reducing the length of the message.

It is also an object of the invention to provide a correspondinglyimproved communication and/or control apparatus.

SUMMARY OF THE INVENTION

The object is achieved with the method of the generic type by means ofthe following steps:

-   -   a message which is currently being transmitted by a transmitting        communication and/or control apparatus is compared with a        previously transmitted message, and    -   it is determined that there is no locking state in the        transmitting communication and/or control apparatus if the        messages are different, and    -   the transmitting communication and/or control apparatus codes a        message counter into the actual message being transmitted if the        messages are the same, and    -   the message counter is decoded in a communication and/or control        apparatus that receives the message, and    -   it is determined that there is no locking state in the        transmitting communication and/or control apparatus if the value        of the message counter has changed in comparison with a previous        value of the message counter in a previously transmitted        message, and    -   a locking state in the transmitting communication and/or control        apparatus is determined if the value of the message counter has        not changed after a defined waiting time.

Instead of the previous additional information, it is thus now proposedto first of all check the changes in the message from one transmissionsequence to the next. If the message changes, the transmittingcommunication and/or control apparatus cannot be in a locking state(deadlock). If the message contents are constant on account of theoperating state, a message counter is preferably coded into the actualmessage being transmitted after a defined or variable initiation time,so that the message area for an additional signal can be dispensed with.A locking state can then be detected by decoding the message counter andevaluating the latter.

The message counter is preferably coded into the message by changing thecoding for a defined bit section of the digital message. If a change inthe coding is detected in the particular bit section, the message beingtransmitted is correct and the communication and/or control apparatus isnot in a locking state. Otherwise, if there is no change in the codingin the particular bit section, it can be concluded, after a definedwaiting time, that a locking state is present.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference tothe accompanying drawings, in which:

FIG. 1 shows a sketch of a motor vehicle having a data bus anddistributed communication and/or control apparatuses;

FIG. 2 shows a signal block of a message which is being transmitted andhas additional information for identifying a possible locking state;

FIG. 3 shows signal blocks of a message which is being transmitted andhas a message counter coded into the message after an initiation timehas elapsed.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 reveals a sketch of a motor vehicle 1 having a data bus 2 towhich a multiplicity of communication and/or control apparatuses SG_(i)(where i=1 . . . N) are connected. Such communication and/or controlapparatuses SG_(i) may be, for example, airbag control apparatuses,wheel sensors, antilock braking system control apparatuses or the like.Since these communication and/or control apparatuses SG_(i) are criticalto safety under certain circumstances, their operational capability mustbe continuously monitored. In particular, locking states in whichprocesses which are carried out or monitored by the communication and/orcontrol apparatuses SG_(i) block one another are critical to safety.

FIG. 2 reveals a signal block for transmitting a message together withan item of additional information in a conventional manner, for examplein the form of a message counter. The additional information in the formof alive bits, which are not used to transmit function signals, is usedto monitor the functionality of the transmitting communication and/orcontrol apparatus SG_(i).

FIG. 3 reveals signal blocks as are used in the inventive method fordetecting locking states.

A signal block comprises only the actual message being transmitted, ifappropriate with additional control information but without alive bitsfor monitoring the functionality of the transmitting communicationand/or control apparatus SG_(i).

In a step which is continuously repeated, the message which is currentlytransmitted by a transmitting communication and/or control apparatusSG_(i) is compared with a previously transmitted message. If themessages are different, it is not possible for a locking state to bepresent in the transmitting communication and/or control apparatusSG_(i).

If the messages are the same, the transmitting communication and/orcontrol apparatus codes a message counter into the actual message beingtransmitted after an initiation time t_(A) has elapsed.

Since the message can be the same an account of a system state thatremains the same or on account of a locking state, the message counteris subsequently monitored. To this end, the message counter is decodedin the communication and/or control apparatus SG_(i) that receives themessage and, if the message counter changes, it is determined that thereis no locking state in the transmitting communication and/or controlapparatus SG_(i). Otherwise, a locking state in the transmittingcommunication and/or control apparatus SG_(i) is detected after adefined waiting time.

The message counter is coded into the message by changing the coding fora defined bit section. If a change in the coding for the particular bitsection is detected by the receiving communication and/or controlapparatus SG_(i), there is no locking state. Otherwise it can beconcluded, after a defined waiting time t_(w), that there is a lockingstate.

1-4. (canceled)
 5. A method for detecting locking states in electronicdevices (SG_(i)) which are networked to one another in a distributedmanner using a data bus (2), comprising the following steps: comparing acurrent message, which is transmitted by at least one of the electronicdevices (SG_(i)) with a previously transmitted message; determining thatthere is no locking state in the transmitting electronic device (SG_(i))if the messages are different; in the transmitting electronic device,coding a message counter into the actual message being transmitted ifthe messages are the same; decoding the message counter in theelectronic device (SG_(i)) that receives the message; determining thatthere is no locking state in the transmitting electronic device (SG_(i))if the value of the message counter has changed in comparison with aprevious value of the message counter in a previously transmittedmessage, and determining a locking state in the transmitting electronicdevice (SG_(i)) if the value of the message counter has not changedafter a defined waiting time (t_(w)).
 6. The method as claimed in claim5, characterized in that the message counter is coded after a definedinitiation time (t_(A)).
 7. The method as claimed in claim 5, whereinthe message is a digital message and message counter is coded into themessage by changing the coding for a defined bit section of the digitalmessage.
 8. An electronic device (SG_(i)) capable of communicating withother electronic devices by means of digital messages via a data bus(2), the electronic device being set up to code a message counter into amessage being transmitted if the message is the same as a previous onetransmitted by the electronic device and to decode from a receivedmessage a message counter previously coded into the received message byanother electronic device.